Field emission electron sources, often referred to as field emission materials or field emitters, can be used in a variety of electronic applications, e.g., vacuum electronic devices, flat panel computer and television displays, emission gate amplifiers, and klystodes. Field emitters of etched silicon or silicon microtips have been known (see Spindt et al., "Physical Properties of Thin Film Field Emission Cathodes", J Appl. Phys., vol. 47, pp. 5248, 1976), but require expensive and elaborate fabrication techniques. Additionally, such field emission cathodes suffer from relatively short lifetimes due to erosion of the emission surfaces from positive ion bombardment.
Others have deposited diamond coatings on silicon surfaces to use the intrinsic electronic properties of diamond, i.e., its negative or low electron affinity. Negative electron affinity means that conduction electrons can easily escape from a diamond surface into vacuum. For example, diamond has been deposited by chemical vapor deposition (CVD) upon silicon substrates for formation of field emitters (see Geis et al., "Diamond Cold Cathode", IEEE Electron Device Letters, vol. 12, no. 8, pp. 456-459, 1991). However, these attempts have yielded low current densities, estimated from about 0.1 to 1 amperes per square centimeter (A/cm.sup.-2) for a diode current of 10 milliamperes (mA), these current densities requiring a high voltage for initial electron emission and accordingly, high power consumption. Recently, amorphic diamond thin films have been deposited upon substrates such as chrome or silicon by laser ablation (see Kumar et al., SID 93 Digest, pp. 1009-1011, 1993) to form field emitters. These field emitters have achieved current densities exceeding those achieved by the earlier etched silicon or silicon microtips, and have achieved light emission from a phosphor bombarded by electrons from such a diamond coated field emitting surface. In one such coating of diamond by CVD upon a silicon or molybdenum substrate, it was found that graphite impurities or graphite particle-like inclusions present from the diamond deposition may have resulted in improved field emission (see Wang et al., Electronics Letters, vol. 27, no. 16, pp. 1459-1461 (1991)).
Further work employing diamond in field emitters has been by Jaskie and Kane (see U.S. Pat. Nos. 5,129,850; 5,138,237; 5,141,460; 5,256,888; and 5,258,685). They describe, e.g., forming field emission electron emitters by providing a selectively shaped conductive/semiconductive electrode having a major surface, implanting ions as nucleation sites onto at least a part of the major surface of the conductive/semiconductive electrode, and growing diamond crystallites at some of the nucleation sites, to produce an electron emitter including a coating of diamond disposed on at least a part of the major surface of the selectively shaped conductive/semiconductive electrode. These emitters are essentially a Spindt-type microtip or cathode overcoated with diamond film. Also, Dworsky et al. (U.S. Pat. No. 5,180,951) have described an electron emitter employing a polycrystalline diamond film upon a supporting substrate of, e.g., silicon, molybdenum, copper, tungsten, titanium and various carbides, with the surface of the diamond film including a plurality of 111 crystallographic planes of diamond or 100 crystallographic planes to provide a low or negative electron affinity. Dworsky et al. teach that the supporting substrate can be substantially planar thereby simplifying the fabrication of the electron emitter.
Despite the recent advances, further improvements in current densities and electron emission efficiency of field emission electron emitters are believed necessary to reduce power consumption requirements in most applications. Other improvements are needed in reproducibility of the emitters, in the lifetimes of the emitters and in reduced fabrication costs of the emitters.
It is an object of the present invention to provide a field emitter material having high electron emission efficiency and low voltage requirements, i.e. low voltage switch-on requirements.
Another object of the present invention is to provide a field emitter material having a longer lifetime or longer period of operation in the face of positive ion erosion.
A further object of the present invention is to provide an easily fabricated field emitter.
Still another object of the present invention is to provide field emitter materials suitable for providing a variety of field emitter cathode geometries.